The law firm's work in activism appears to be growing as the strategy is becoming increasingly popular with investors.

Steven Wolosky, a partner and chair of the activist- and equity-investment practice at Olshan, told Business Insider in August that most of his clients are focused on operational activism rather than turning a quick buck.

Activists are now acting almost like private-equity firms, performing diligence on a deal and looking to market their viewpoints to institutional investors, he said.

"It's beyond the performance of the company," said Wolosky. "It's beyond the CEO's performance."

The rise in activism has placed a premium on legal expertise. Hedge funds and big banks alike are eager to bring experts into their ranks to ready defenses in increasingly costly campaigns to control boards' independence.